It's Awkward
So is trying to use a 5-pound 15" notebook while walking somewhere. iPad isn't made for desktop use, it's made for "always around", a convenient size to have handy. Maybe not real comfortable, but much better in more situations.
It's heavy
Got something lighter with a screen over 9"?
It's slippery
May be a valid complaint. Well, it IS so slick in so many ways...
The screen has too much glare
We've been hearing that whine since CRTs got flat.
Forget reading in the sun
Forget reading your Kindle in the dark. Actually, IIRC the iPad is at least pretty usable in bright sun (a la the iPod Touch/iPhone) - not great, but there if you need it.
Fingerprints are annoying
Keep yer paws off it then. Oh, right, it's a touch-screen ... you're going to get fingerprints on it.
It does not multitask
"Multitask" is an awfully broad term. Few whiners really want it, they just want to whine about it and would be content with mere task switching (coming soon!).
The browser is limited
It's a 1.5lb 10" no-keyboard 1/2" thick tablet, not a full-blown desktop. Cope.
The virtual keyboard stinks
So do real keyboards. Maybe it's that keyboards are unnatural. If you need one, just bring it near your Bluetooth keyboard and type away.
There's no USB port
It's a USB device, not a host.
iPhone-only apps look horrible
So does VHS on a 55" plasma HDTV, and for the same reason.
The price is just too high
Slightly more than the full-sale no-contract price of upper-end cell phones - and it is a lot bigger and does a lot more than a cell phone. Netbooks are cheaper, but they're different products built cheaply with problems that are not inexpensive to solve (which the iPad solves, at a price).
It doesn't replace anything
It's not supposed to. It's a new genre. It's not a phone. It's not a notebook. It's not a netbook. It's not a iPod. It's a slate done right.
Could you explain,”it’s a USB device, not a host?”